A jerky treat recall, issued in January in an attempt to find out the cause of a huge wave of illnesses among pets, has still not resulted in the reason for hundreds of deaths being found. According to reports about 600 pets have died and more than 3,600 have been taken seriously ill, and until now health officials are still at a loss in solving the mystery.

A Jerky Treats recall was made in January but health officials are still finding it a mystery as to why 600 pets have died and 3,600 others have been taken seriously ill.

The deaths have allegedly been tied to jerky treats made in China, and illnesses have been found in animals who have eaten the snack for years. The rate of illnesses has slowed this year, according to health officials, however, the federal Food and Drug Administration officials are now calling on veterinarians and pet owners to help solve the mystery.

"To date, testing for contaminants in jerky treats has not revealed a cause for the illnesses," Martine Hartogensis, a deputy director for the FDA's Center for Veterinary Medicine, said in a report. "Despite these warnings, we have continued to receive reports of illnesses in both cats and dogs."

Earlier this year in January, the FDA reported that 500 animals had been killed and 3,200 sickened – allegedly connected to the jerky treats. Since then the rate of deaths has fallen sharply thanks to a jerky treats recall from two of the largest sellers.

Several brands have taken part in the recall, including Waggin' Train and Canyon Creek Ranch treats made by Nestle Purina PetCare Co. and Milo's Kitchen Chicken Jerky and Chicken Grillers home-style dog treats from Del Monte Corp.

Reports have confirmed that various pet owners have been reporting illness and death among their pets since 2007, with various health issues identified including gastrointestinal and kidney failure.

Officials have been investigating the cause for months now but are still not closer to finding out why the jerky treats are causing the problems.

"We still are extensively testing treats for a number of things," Hartogensis told NBC News. "We do seem to be getting some leads, but we still have a little bit of a ways to go."

The FDA has asked veterinarians to send detailed information about the cats and dogs that become sick after eating the jerky treats.